Hubble constant in the axi-Higgs universe

Abstract

The Λ-cold-dark-matter (ΛCDM) model provides an excellent fit to the cosmic microwave background (CMB) data. However, a statistically significant tension emerges when its determination of the Hubble constant H_{0} is compared to the local distance-redshift measurements. The axi-Higgs model, which couples an ultralight axion to the Higgs field, offers a specific variation of the ΛCDM model. It relaxes the H_{0} tension as well as explains the ^{7}Li puzzle in big bang nucleosynthesis, the clustering S_{8} tension with the weak-lensing (WL) data, and the observed isotropic cosmic birefringence in CMB. In this Letter, we demonstrate how the H_{0} and S_{8} tensions can be relaxed simultaneously, by correlating the axion impacts on the early and late universe. In a benchmark scenario (m=2×10^{−30} eV) selected for upcoming experimental tests, the analysis combining the CMB+BAO (baryon acoustic oscillation)+WL+SN data yields H_{0}=69.9±1.5 km/s/Mpc and S_{8}=0.8045±0.0096. Combining this [excluding the SN (supernovae) part] with the local distance-redshift measurements yields H_{0}=72.42±0.76 km/s/Mpc, while S_{8} is slightly more suppressed.